Validate that the codec is functional before using it. Fixes streaming failure with VAAPI if hardware lacks codec support

app/streaming/video/ffmpeg-renderers/vaapi.h

@@ -38,6 +38,10 @@ public:
     virtual void renderFrame(AVFrame* frame);
 
 private:
+    static
+    enum AVPixelFormat ffGetFormat(AVCodecContext*,
+                                   const enum AVPixelFormat* pixFmts);
+
     Window m_XWindow;
     AVBufferRef* m_HwContext;
     void* m_X11VaLibHandle;